Characterization of T-cell lymphoproliferative process in lymph node. (A) Architecture is diffusely infiltrated by small lymphocytes with admixed histiocytes. (B) In situ hybridization with an EBV-encoded RNA (EBER) probe shows rare positive small lymphocytes (< 1 per high power field) that correspond to the distribution of B cells in the same area. (C) CD20 stain shows scattered small positive lymphocytes and small aggregates, but absence of follicular structures. The majority of the lymphocytes are CD3⁺ (D), with a predominance of CD8⁺ cells (E), over CD4⁺ cells (F). Numerous lymphocytes are granzyme B positive (G), but negative for perforin (antibody KM585-P1-8; Kamiya Biochemical, Seattle, WA) (H). Inset in panel H shows positive perforin control in a patient with large granular lymphocyte leukemia. Original magnification, × 400, except panel C (× 250) and panel H inset (× 1000).